nouveau/gsp: convert gsp errors to generic errors

This should let the upper layers retry as needed on EAGAIN.

There may be other values we will care about in the future, but
this covers our present needs.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231222043308.3090089-8-airlied@gmail.com